Starting with Windows 8, your phone can now be recognized as Portable Player (USB Mass Storage) on a Windows PC. This in turn, gives you access to Mass Storage drive of Windows Phone right in your windows explorer. This makes it lot easier for you copy files in & out of Windows Phone without the need of any application.
Steps to enable Mass Storage:
Actually there is no step but here is what you need to. Connect your phone with your PC via USB cable and your phone will be detected as Portable Player. In case you have the App installed, it will be displayed as Windows Phone.
Double click on that and it will display the storage device, named as Phone as USB device.
What’s inside the Storage Drive?
Documents: Any file, which you have, saved to phone will show up here. However PDF files still don’t show up here as there is no save to phone option with default PDF reader from Microsoft. However, you can read and view the docs from there.
Music: This is a bit different from rest as you have folders like Album, Artist, Playlist and Podcast Series. So if you want to do it right, drop the music files into the Album Folder and the rest will take care by the Windows Phone Music App.
Ringtones: This special folder makes it easy for you to copy any MP3 file and set it as ringtone on your Windows Phone. Yes, you can have custom ringtone on your Windows Phone. The songs, which you copy, here appear under Custom Label in Ringtones and will work only if the audio file is DRM free and smaller than 30MB, it can be used as custom ringtone.
The Video and image folders are pretty simple. All you need is add files to it and it will show up in its respective section i.e. Picture Library & Music + Video App.